This invention relates to an apparatus for contacting fluids in a fluid-solids contacting zone such as an adsorption zone or a reaction zone. More particularly, the invention is directed to the contacting of two fluids comprising a liquid phase and a vapor phase in a fluid-solids contacting zone, and to means and methods for effecting improved heat exchange between the vapor and liquid phases in the contacting vessel. More specifically, the invention relates to a new and improved method and apparatus for uniformly distributing a liquid phase into a flowing liquid, vapor, or mixed liquid-vapor phase in a granular or particulate solids contacting zone, as in an adsorption tower or in a catalytic reactor such as a catalytic condensation reactor.
Many of the most important commercial hydrocarbon conversion processes involve the physical or chemical treatment of hydrocarbons and other organic materials with beds of granular or particulate solid contact materials. Many of these processes involve contacting two fluids with the contact materials. Often one of the fluids comprises a liquid phase while the other fluid comprises a gas or vapor phase, a liquid phase, or a mixed vapor-liquid phase. It is well known that introducing a liquid phase into either a gas or vapor phase or a mixed vapor-liquid phase, and in a manner that achieves uniform distribution, is difficult to attain.
A typical process wherein uniform distribution of liquid and gas phases, or of liquid and mixed gas-liquid phases, is necessary but infrequently achieved, is that of catalytic condensation. The chemical processing industry uses the catalytic condensation process to produce transportation fuels, olefinic petrochemicals such as octene and nonene, and alkyl aromatic hydrocarbons such as cumene, that are sold in bulk as commercial commodities. When producing transportation fuels or olefinic petrochemicals, the catalytic condensation process oligomerizes olefins in the presence of a particulate solid catalyst, and the process is known within the industry as catalytic polymerization or as simply xe2x80x9ccat poly,xe2x80x9d with the resulting motor fuel, which may comprise dimers, trimers, and tetramers, often referred to as polymer gasoline. The feed to such a catalytic condensation reaction zone typically comprises propylene and butylene, although propane and butane may also be present. Prevailing conditions in the reaction zone are generally vapor phase at relatively low reaction pressures, or a dense fluid phase or a mixed vapor-liquid phase at a higher pressures. When producing alkyl aromatics, the catalytic condensation process alkylates aromatic hydrocarbons with olefins in the presence of a particulate solid catalyst, and generally the reactants and products within the reaction zone are vapor-phase.
It is also well known that both the oligomerization and alkylation reactions that occur in the presence of the solid catalyst are exothermic, and that the temperature of the phase or phases in contact with the catalyst increases due to the exothermic heat of reaction. Excessive temperatures within the catalyst bed, however, can adversely affect the select physical and chemical properties of the catalyst and can lead to the formation of reaction byproducts. In order to avoid these undesirable consequences, it is typical to arrange the catalyst in a plurality of separate fixed beds so that diluent or quench liquids may be distributed between the beds during the reaction. In the case of olefin oligomerization, the cool quench liquids may comprise one or more of the olefin reactants and/or one or more paraffins having the same number of carbon atoms as the olefin reactants. In the case of aromatic alkylation, the cool quench may comprise one or more of each of the olefin reactants, paraffins, or aromatic reactants. The cool quench liquids reduce the temperature of the effluent from one bed of catalyst prior to feeding the mixture of effluent and quench liquid to the next bed of catalyst.
It is typical in the art of catalytic condensation to support each individual bed of catalyst upon a perforated support plate or grid deck. It is also typical in the art to introduce the quench liquid between the fixed beds of catalyst by means of a single nozzle attached to a single pipe. The quench liquid is introduced through an inlet port or opening in the reactor vessel wall into one end of the pipe, which is mounted to the inlet port via a flanged connection on the outside wall of the reactor vessel. The pipe extends into the reactor vessel, so that the nozzle attached to the end of the pipe is at the quench point, a position in the cross-section of the vessel where discharge of the quench liquid is desired. Typically, the quench point is at the center-point of the cross-section. It is typical first to assemble the pipe and nozzle assembly outside of the reactor vessel, and then to insert, or stab in, the assembly through the inlet port. The dimensions of the opening of the inlet port are typically only slightly greater than that needed to allow the pipe with its attached nozzle to pass through. This arrangement allows the pipe and nozzle assembly to be inserted into or withdrawn from the reactor vessel even when the grid decks are in place and the beds are fully loaded with catalyst. Using this arrangement, assembly or disassembly of the pipe or nozzle within the reactor vessel does not require reactor maintenance workers to enter between the beds. This is an important consideration in catalytic condensation processes, especially during loading and unloading of the catalyst beds, when such assembly or disassembly would be difficult and time-consuming. In fact, this consideration precludes the use in catalytic condensation reactor vessels of large distributor grids consisting of multiple perforated pipe branches that are positioned throughout the entire cross-section, since such complex distributors would require unacceptable difficulties and delays for assembly and disassembly.
A fluid distributing apparatus in a catalytic condensation reactor is used with the intent of achieving a complete distribution of the quench liquid as uniformly as possible throughout the cross-sectional area of the reactor vessel and of the catalyst bed below. It is also the purpose of the apparatus that the effluent from the catalyst bed above flows down from the perforated support plate throughout the cross-sectional area of the reactor while the quench liquids is distributed by the single nozzle and plate assembly throughout the cross-sectional area of the reactor vessel. Further, it is the purpose of fluid distributing apparatus to provide an intimate contact between the cooled quench and the hot effluent from the bed above the fluid distributing apparatus in order to achieve a uniform temperature of the components that are fed to the bed below the fluid distributing apparatus.
However, the prior art fluid distributing apparatus comprising a single nozzle attached to a single pipe has proven to be relatively ineffective in accomplishing these objectives. Achieving these objectives is made difficult by the fact that it is typical to add a relatively small amount of cool quench liquids to a relatively large quantity of hot effluent which is leaving the bed above at an elevated temperature. The difficulty is further complicated by the fact that the amount of cool quench is relatively small in relation to the large cross-sectional area of the reactor vessel which must be covered in order to maintain a proper uniform distribution of the phase or phases present to the bed of catalyst below. In addition, the amount and composition of quench material injected after any particular bed may be varied according to need, which depends in large part on the amount of heat of reaction to be dissipated. For example, a recently-loaded catalyst bed containing highly active fresh catalyst may generate a relatively large heat of reaction, but the same catalyst bed after several months of operation may contain partially deactivated catalyst and may generate relatively little heat of reaction. In order to maintain the desired inlet temperature of the catalyst bed below a catalyst bed that is generating less heat of reaction, the flow of quench material between the two catalyst beds must be decreased. However, experience with commercial nozzles has shown that it is typical that even only a 30% decrease in the flow rate of quench fluid from a nozzle""s design rate causes a significant deterioration in the nozzle""s capability to distribute fluid across the cross-section of the reactor. The result is that the temperature encountered within the catalyst bed below will be quite uneven, and localized undesirable hot spots are often found in the bed below. It is well-known by those skilled in the art that the existence of hot spots within the catalyst bed leads to indiscriminate and nonselective reactions of the reactants, which is an undesirable result.
Accordingly, an improved apparatus and an improved method for contacting fluids in a fluid-solids contacting chamber are sought that can provide uniform distribution of fluid flow, even at relatively low flow rates, so as to prevent the problems associated with high temperatures in catalyst beds.
This invention is an improved apparatus and method for contacting fluids that can be readily and inexpensively employed to provide uniform distribution of fluid flow in or between particulate solid beds of a fluid-solids contacting chamber, even at relatively low flow rates. This invention solves the problems associated with maldistribution of fluid in such solid beds that arise from the inefficiency of nozzles when operated at flow rates that are significantly lower than their design flow rates. Compared to the apparatus of the prior art, the apparatus of this invention incorporates one or more additional conduits and outlet ports that are capable of providing improved fluid distribution. The additional conduit(s) are arranged within a single conduit, to which the additional outlet port(s) are also attached, in a manner which allows the assembly of the plurality of conduits and outlet ports to be extended into the fluid-solids contacting chamber through an opening or port in the chamber wall that is, in some embodiments of this invention, either the same size or insignificantly larger than that through which the single conduit, with its single outlet port, is extended. Thus, the apparatus of this invention can be inserted into or withdrawn from the space between beds of the fluids-solid contacting chamber, even when access between the beds is restricted, such as when the beds are fully loaded with solids. The method of this invention can be practiced using inexpensive manual valves to increase or decrease the flow of fluid to the plurality of nozzles. In addition to these advantages of low apparatus cost and ease of operation, this invention also can increase significantly the time period between shutdowns of the fluid-solids contacting chamber, thereby greatly improving the efficiency and profitability of operating fluid-solids contacting chambers, particularly catalytic condensation reactors.
Accordingly, in an apparatus embodiment, this invention is a fluid-solid contacting chamber. Within the chamber, which has a chamber wall, is positioned a first bed that holds and retains particulate solids. A second bed which holds and retains particulate solids is also positioned within the chamber. Together, the chamber wall, the first bed, and the second bed define at least in part an interbed space that is within the chamber. The chamber also comprises an outer conduit connected to the chamber wall. A first inlet port is connected to the outer conduit for introducing fluid into the outer conduit. A first outlet port is connected to the outer conduit and in fluid communication with the interbed space for discharging fluid from the outer conduit and into the interbed space. An inner conduit is positioned within the outer conduit. The inner conduit has an inner conduit wall, and the inner conduit wall and the outer conduit define at least in part an outer space. The outer space is in fluid communication with the first inlet port and the first outlet port. The inner conduit wall defines at least in part an inner space within the inner conduit. A second inlet port is connected to the inner conduit for introducing fluid into the inner conduit, and the second inlet port is in fluid communication with the inner space. A second outlet port is connected to the inner conduit and in fluid communication with the inner space and the interbed space for discharging fluid from the inner space and into the interbed space.
In one of its method embodiments, this invention is a method of mixing fluids in a fluidsolid contacting chamber. An effluent is withdrawn from a first bed containing particulate solids in a fluid-solid contacting chamber. The effluent passes into an interbed space within the chamber, and the interbed space is defined in part by the first bed and the wall of the contacting chamber. A first quench fluid passes into an inlet end of a first quench conduit, and the first quench fluid is discharged from an outlet end of the first quench conduit into the interbed space at a first flow rate. After passing the first quench fluid at the first flow rate, the flow rate of the first quench fluid is decreased to a second flow rate that is less than the first flow rate. Also, after passing the first quench fluid at the first flow rate, a second quench fluid passes into an inlet end of a second quench conduit, and the second quench fluid is discharged from an outlet-end of the second quench conduit at a third flow rate that is less than the first flow rate. The second quench fluid passes through an interconduit space, which is defined by the wall of the first quench conduit and the wall of the second quench conduit. After passing the second quench fluid at the third flow rate, the flow rate of the second quench fluid is decreased to a fourth flow rate that is less than the third flow rate. The effluent is contacted with at least one of the first quench fluid and the second quench fluid in the interbed space to produce a mixture, which passes to a second bed containing particulate solids in the fluid-solid contacting chamber.